Dual solder methodologies for ultrahigh density first level interconnections

ABSTRACT

An apparatus, comprising an integrated circuit (IC) package having at least one solder bond pad, a die having at least one solder bond pad, wherein the die is bonded to the IC package by at least one solder joint between the at least one solder bond pad of the die, and the at least one solder bond pad of the IC package, and an underfill material between the IC package and the die, wherein the at least one solder joint is embedded in the underfill material, and wherein the at least one solder joint comprises a first metallurgy and a second metallurgy.

BACKGROUND

As increasing demands are placed on microelectronics packagingtechnologies to scale down package footprint and thickness, interconnectdimensions must also be scaled down. As first level interconnect (FLI)pitches decrease for building ultrahigh density architectures,challenges arise for bonding integrated circuit dies to packagesubstrates. One problem is the incidence of solder bridge formation.Another problem are low yields of finished packages due towarpage-associated incomplete solder joint formation (e.g., non-contactopens) between bond pads on both die and substrate during thermalcompression bonding operations.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the disclosure will be understood more fully from thedetailed description given below and from the accompanying drawings ofvarious embodiments of the disclosure, which, however, should not betaken to limit the disclosure to the specific embodiments, but are forexplanation and understanding only.

FIG. 1 illustrates a cross-sectional view of a first embodiment of apackage having a dual solder joint embodiment between a die andsubstrate having an underfill, according to some embodiments of thedisclosure, according to some embodiments of the disclosure.

FIGS. 2A-2G illustrate cross-sectional views, respectively, of a firstembodiment of a method for fabricating a package having a dual solderjoint embodiment between a die and substrate having an underfill,according to some embodiments of the disclosure.

FIGS. 3A-3F illustrate cross-sectional views, respectively, of a secondembodiment of a method for fabricating a package having a dual solderjoint embodiment between a die and substrate having an underfill,according to some embodiments of the disclosure.

FIG. 4 illustrates a cross-sectional view of a second embodiment of apackage having a dual solder joint embodiment between a die and asubstrate, without an underfill, according to some embodiments of thedisclosure.

FIGS. 5A-5D illustrate cross-sectional views, respectively, of a methodfor fabricating a package having a dual solder joint embodiment betweena die and a substrate, without an underfill, according to someembodiments of the disclosure.

FIG. 6 illustrates a package having a dual solder joint embodimentbetween a die and a substrate, fabricated according to the disclosedmethod, as part of a system-on-chip (SoC) package in an implementationof computing device, according to some embodiments of the disclosure.

DETAILED DESCRIPTION

In the following description, numerous details are discussed to providea more thorough explanation of embodiments of the present disclosure. Itwill be apparent, however, to one skilled in the art, that embodimentsof the present disclosure may be practiced without these specificdetails. In other instances, well-known structures and devices are shownin block diagram form, rather than in detail, in order to avoidobscuring embodiments of the present disclosure.

Here, the term “package” generally refers to a self-contained carrier ofone or more dies, where the dies are attached to the package substrate,and encapsulated for protection, with integrated or wire-bonedinterconnects between the die(s) and leads, pins or bumps located on theexternal portions of the package substrate. The package may contain asingle die, or multiple dies, providing a specific function. The packageis usually mounted on a printed circuit board for interconnection withother packaged Integrated Circuit (ICs) and discrete components, forminga larger circuit.

Here, the term “dielectric” generally refers to any number ofnon-conductive materials that make up the structure of a packagesubstrate. For purposes of this disclosure, dielectric material may beincorporated into an IC package as layers of laminate film or as a resinmolded over IC dies mounted on the substrate.

Here, the term “metallization” generally refers to metal layers formedover the dielectric material of the package substrate. The metal layersare generally patterned to form metal structures such as traces and bondpads. The metallization of a package substrate may be confined to asingle layer or in multiple layers separated by layers of dielectric.

Here, the term “bond pad” generally refers to metallization structuresthat terminate integrated traces and vias in microelectronic packagesand dies.

Here, the term “solder bump” generally refers to a solder layer formedon a bond pad. The solder layer typically has a round shape, hence theterm “solder bump”.

Here, the term ‘liquidus” generally refers to the liquid state of amolten metallic mixture, such as solder. There is no specific meltingpoint as the solder melts over a temperature range. The liquidus stateis the state where the mixture is completely melted.

Here, the term “solidus” generally refers to the solid state of a solidmetallic mixture, such as solder. As for the liquidus state, there is nospecific solidification temperature as the liquid mixture solidifiesover a temperature range. The solidus temperature is the temperaturewhere the mixture is completely solidified.

Here, the term “metallurgy” generally refers to an alloy composition. Inthis disclosure, “metallurgy” is used to represent solder alloycompositions, for example.

Disclosed herein is a method for a touch and bond dual solder metallurgyon the die and package substrate, and structures made by the disclosedmethod. The method comprises a touch-and-bond process, where two solderlayers are deposited on bond pads of a die and a package substrate. Thesolder layers have different compositions having disparate liquidustemperatures. In some embodiments, the two solder layers are formedseparately, where a first solder layer comprising a solder compositionhaving a first liquidus temperature T_(L1) is deposited on the die, anda second solder layer comprising a solder composition having a secondliquidus temperature (T_(L2), where T_(L2) is greater than T_(L1)) isdeposited on the substrate. The solder layers are then joined byjuxtaposing the bond pads of the die and substrate.

In some embodiments, the two solder layers are formed in succession onthe bond pads of the die or on the substrate. In some embodiments, thefirst solder layer is formed on bond pads of the substrate, then heatedto a temperature where an intermetallic compound (IMC) is formed betweenthe material of the bond pad (e.g., copper) and one or more metalelements of the solder layer (e.g., tin). The IMC has a melting pointsignificantly higher than the liquidus temperatures of the two soldercompositions.

The second solder layer is formed on the bond pads of the die. Bond padsof the die and the substrate are juxtaposed. According to someembodiments, the juxtaposed bond pads on the die and substrate arecontacted under pressure and heated. As an example, the die andsubstrate are brought into contact in a thermal compression bonding(TCB) tool. The temperature is raised to the first (e.g., lower)liquidus temperature, where the first solder layer melts and is reflowedto form partial solder joints between the bond pads of the die andsubstrate. According to embodiments, the volume of the solder containedwithin the first solder layer is relatively low relative to the volumeof solder contained within the second solder layer. As a result, thepartial solder joints are small, and form a temporary bond between thedie and substrate. The temporary bond serves to hold the die andsubstrate together as a mechanically stable unit for further processingbefore a complete solder joint is formed. The second solder layerremains intact, as the first temperature is too low to melt secondlayer.

As pointed out above, solder bridging is a common occurrence whenbonding (e.g., flip-chip bonding) dies and substrates designed withhigh-density FLI architectures. In some embodiments, an underfillmaterial is injected between the die and the substrate then cured,embedding the partial solder joints in the underfill material. Theembedded partial solder joints comprise the intact second solder layer.In a subsequent operation, the partial solder joints are heated to thesecond liquidus temperature (T_(L2)) or above, where the second solderlayer is melted and reflowed to form a permanent solder joint betweenthe bond pads of the die and the substrate. During reflow of the secondsolder layer, the melt is confined within a cavity within thesurrounding underfill material, the larger volume of liquid solder(relative to the first solder layer volume) not able to flow over to theneighboring bond pad pair. In this way, solder bridging is eliminated.

In an alternative embodiment, the second solder layer is formed on thebond pads of the substrate. The second solder layers formed onindividual bond pads may take on the shape of a ball or a bump.Typically, the height of the bumps as formed may vary in thicknesses oneach bond pad by 10-20%. This variation may translate to differences insolder bumps by as much as 10 microns. While natural warpage is presentin the die and substrate, if bonded in a TCB or similar tool, thesubstrate and die are held flat. However, the variation in bump heightcan result in some non-contact opens (NCOs), or failure to form solderjoints between some of the bond pad pairs.

To avoid the variation of solder bump height, the solder bumps areflattened by pressing the solder bumps, for example, in a TCB tool, tolevel the bumps to a substantially equal height before subsequentbonding operations.

Throughout the specification, and in the claims, the term “connected”means a direct connection, such as electrical, mechanical, or magneticconnection between the things that are connected, without anyintermediary devices.

The term “coupled” means a direct or indirect connection, such as adirect electrical, mechanical, or magnetic connection between the thingsthat are connected or an indirect connection, through one or morepassive or active intermediary devices.

The term “circuit” or “module” may refer to one or more passive and/oractive components that are arranged to cooperate with one another toprovide a desired function. The term “signal” may refer to at least onecurrent signal, voltage signal, magnetic signal, or data/clock signal.The meaning of “a,” “an,” and “the” include plural references. Themeaning of “in” includes “in” and “on.”

The vertical orientation is in the z-direction and it is understood thatrecitations of “top”, “bottom”, “above” and “below” refer to relativepositions in the z-dimension with the usual meaning. However, it isunderstood that embodiments are not necessarily limited to theorientations or configurations illustrated in the figure.

The terms “substantially,” “close,” “approximately,” “near,” and“about,” generally refer to being within +/−10% of a target value(unless specifically specified). Unless otherwise specified the use ofthe ordinal adjectives “first,” “second,” and “third,” etc., to describea common object, merely indicate that different instances of likeobjects are being referred to, and are not intended to imply that theobjects so described must be in a given sequence, either temporally,spatially, in ranking or in any other manner.

For the purposes of the present disclosure, phrases “A and/or B” and “Aor B” mean (A), (B), or (A and B). For the purposes of the presentdisclosure, the phrase “A, B, and/or C” means (A), (B), (C), (A and B),(A and C), (B and C), or (A, B and C).

Views labeled “cross-sectional”, “profile” and “plan” correspond toorthogonal planes within a cartesian coordinate system. Thus,cross-sectional and profile views are taken in the x-z plane, and planviews are taken in the x-y plane. Typically, profile views in the x-zplane are cross-sectional views. Where appropriate, drawings are labeledwith axes to indicate the orientation of the figure.

FIG. 1 illustrates a cross-sectional view of a first embodiment ofpackage 100, having a dual solder joint embodiment between a die andsubstrate having an underfill, according to some embodiments of thedisclosure.

In FIG. 1, package 100 comprises die 101 and substrate 102. Solder joint103 is between, and bonded to, bond pad 104 on die 101 and bond pad 105on substrate 102. Solder joint 103 is composed of metallurgies (alloys)that may comprise, but are not limited to, metals such as tin, silver,copper, bismuth, zinc, indium, gold, aluminum, and germanium. In someembodiments, solder joint 103 comprises a compositional gradient of tinconcentration between bond pad 104 and bond pad 105. In someembodiments, solder joint 103 comprises a concentration of tin adjacentto bond pad 104 on die 101 that is higher than the concentration of tinadjacent to bond pad 105 on substrate 102.

In some embodiments, solder joint 103 comprises a compositional gradientof gold concentration between bond pad 104 and bond pad 105. In someembodiments, solder joint 103 comprises a concentration of gold adjacentto bond pad 105 that is higher than the concentration of gold adjacentto bond pad 104.

In some embodiments, solder joint 103 comprises a compositional gradientof gold concentration between bond pad 104 and bond pad 105. In someembodiments, solder joint 103 comprises a concentration of gold adjacentto bond pad 104 that is higher than the concentration of gold adjacentto bond pad 105.

In some embodiments, solder joint 103 comprises a compositional gradientof zinc concentration between bond pad 104 and bond pad 105. In someembodiments, solder joint 103 comprises a concentration of zinc adjacentto bond pad 104 that is higher than the concentration of zinc adjacentto bond pad 105.

In some embodiments, solder joint 103 comprises a compositional gradientof zinc concentration between bond pad 104 and bond pad 105. In someembodiments, solder joint 103 comprises a concentration of zinc adjacentto bond pad 105 that is higher than the concentration of zinc adjacentto bond pad 104.

In some embodiments, solder joint 103 comprises a compositional gradientof aluminum concentration between bond pad 104 and bond pad 105. In someembodiments, solder joint 103 comprises a concentration of aluminumadjacent to bond pad 105 that is higher than the concentration of zincadjacent to bond pad 104.

In some embodiments, solder joint 103 comprises a compositional gradientof aluminum concentration between bond pad 104 and bond pad 105. In someembodiments, solder joint 103 comprises a concentration of aluminumadjacent to bond pad 104 that is higher than the concentration of zincadjacent to bond pad 105.

In some embodiments, underfill 106 is between die 101 and substrate 102.In some embodiments, solder joint 103 is embedded in underfill 106.Underfill 106 may comprise materials comprising proprietary formulationsin products used in microelectronic package assembly. Underfill 106strengthens the solder bonds between die 101 and substrate 102.

FIGS. 2A-2G illustrate cross-sectional views, respectively, of a firstembodiment of a method for fabricating package 100, having a dual solderjoint embodiment between a die and substrate having an underfill,according to some embodiments of the disclosure.

In the operation shown in FIG. 2A, substrate 102 is received. In someembodiments, substrate 102 comprises core 201, dielectric 202 and bondpad 105 embedded in dielectric 202.

In the operation shown in FIG. 2B, first solder bump 203 is formed onbond pad 105. In some embodiments, first solder bump 203 is formed by adeposition process that is any of electroless plating, electrolyticplating (electroplating) or paste printing. Following the depositionprocess, first solder bump 203 is reflowed, according to someembodiments. In some embodiments, first solder bump 203 comprises afirst solder metallurgy composition. According to some embodiments, thez-height of as-deposited first solder bump 203 may vary by as much as20%, for example.

In some embodiments, the first solder metallurgy composition comprisesmixtures comprising any of gold, aluminum, germanium, zinc, tin, bismuthand indium. An exemplary composition of first solder metallurgycomposition may comprise 80% gold and 20% tin. A second examplecomposition of first solder metallurgy may comprise 95% zinc and 5%aluminum. Here, the percentages are based on molar ratios. In someembodiments, first solder bump 203 has a first liquidus that ranges intemperature from 280° C. to 485° C. In some embodiments, the firstliquidus temperature (T_(L1)) of first solder bump 203 is dependent onthe composition of first solder bump 203.

In the operation shown in FIG. 2C, first solder bump 203 is compressedto reduce its z-height to a predetermined value. In some embodiments,substrate 102 is mounted in a thermal compression bonding (TCB) tool andclamped between platens. In some embodiments, first solder bump 203 issoft enough to compress without application of heat. During compression,substrate 102 is held flat, and first solder bump 203 is substantiallyplanarized with other solder bumps on substrate 102. According to someembodiments, die bonding, such as flip-chip bonding, is facilitated asthe probability of contact between individual solder bumps on substrate102 and bond pads or bumps on a die is substantially increased duringdie (chip) bonding in a subsequent operation.

In the operation shown in FIG. 2D, die 101 is received with secondsolder bump 204 formed over bond pad 104 in an earlier operation. Insome embodiments, second solder bump 204 is deposited by one ofelectroless deposition, electrolytic plating or paste printing. In someembodiments, second solder bump 204 has a substantially smaller volumethan first solder bump 203. In the operation shown in FIG. 2D, die 101is aligned with substrate 102 such that first solder bump 203 is alignedand juxtaposed with solder bump 204. In some embodiments, die 101 andsubstrate 102 are mounted in a TCB tool.

In some embodiments, second solder bump 204 comprises a second soldermetallurgy composition. In some embodiments, the second soldermetallurgy composition comprises metals such as, but not limited to,tin, silver, zinc, copper, bismuth and indium. An exemplary compositionof second solder metallurgy composition may comprise 95.5% tin, 4%silver and 0.5% copper. A second example composition of second soldermetallurgy may comprise 89% tin, 8% zinc and 3% bismuth. Here, thepercentages are based on molar ratios. In some embodiments, secondsolder bump 204 has a second liquidus (T_(L2)) that ranges intemperature from 138° C. to 227° C. In some embodiments, the secondliquidus temperature is dependent on the composition of second solderbump 204. In some embodiments, T_(L2) is less than T_(L1).

In the operation shown if FIG. 2E, die 101 is pressed to substrate 102to abut second solder bump 204 against first solder bump 203. In someembodiments, the operation is performed in a TCB tool head. Die 101 andsubstrate 102 are compressed between heated platens. In someembodiments, the temperature of the platens is raised to the secondliquidus temperature T_(L2) or above, but below T_(L1). Second solderbump 204 liquefies and flows at or above T_(L2). In some embodiments,the platen temperature is ramped down to allow second solder bump tore-solidify.

In some embodiments, second solder bump 204 reflows over first solderbump 203, which does not melt during the operation. A metallic bond isformed between first solder bump 203 and second solder bump 204. In someembodiments, the relatively smaller volume of second solder bump 204creates a partial solder joint 205 without flowing to neighboring solderbumps. In this way, solder bridging between neighboring bond pads isprevented or substantially mitigated. In some embodiments, partialsolder joint 205 is temporary, and functions as a tack to hold die 101to substrate 102 during subsequent operations before a permanent solderjoint is formed by the reflow operation of first solder bump 203,described below.

In the operation shown in FIG. 2F, capillary underfill (CUF) 206 isintroduced between die 101 and substrate 102. In some embodiments, CUF206 is injected between die 101 and substrate 102. In some embodiments,CUF 206 is introduced between die 101 and substrate 102 by capillaryaction. Methods to introduce CUF 206 between die 101 and substrate 102are known in the industry, and may be employed to introduce CUF 206.

In some embodiments, CUF 206 protects solder joints and contributes tostiffening the bond between die 101 and substrate 102. According to someembodiments, CUF 206 confines solder from first solder bump 203 frombridging over to neighboring solder bumps, as described below.

In the operation shown in FIG. 2G, the temperature of the platens israised to the first liquidus temperature T_(L1) or above. First solderbump 203 liquefies and flows at or above T_(L1). Simultaneously, secondsolder bump 204 liquefies. In some embodiments, liquid solder fromsecond solder bump 204 blends with liquid solder from first solder bump203. In some embodiments, a compositional gradient forms during reflow,where the elements in first solder bump 203 have a highest concentrationadjacent to bond pad 105 at substrate 102, with a lesseningconcentration toward bond pad 104 at die 101. Conversely, the elementsof second solder bump 204 have a highest concentration adjacent to bondpad 105 at die 101, with a lessening concentration toward bond pad 104at substrate 102. In some embodiments, the composition of the solderhomogenizes during reflow.

As the volume of first solder bump 203 is larger relative to the volumeof second solder bump 204, solder bridging would normally occur withoutthe presence of CUF 206. In some embodiments, CUF 206 confines liquidsolder from molten first solder bump 203 from flowing laterally. In someembodiments, solder bump 203 reflows and blends with solder bump 204, asdescribed above, forming permanent solder joint 207. In someembodiments, the platen temperature is ramped down to allow secondsolder bump to re-solidify.

FIGS. 3A-3F illustrate cross-sectional views, respectively, of a secondembodiment of a method for fabricating package 100, having a dual solderjoint embodiment between a die and substrate having an underfill,according to some embodiments of the disclosure.

In the operation shown in FIG. 3A, die 101 and substrate 102 arereceived. Die 101 comprises bond pad 104, and substrate 102 comprisesbond pad 105.

In the operation shown in FIG. 3B, first solder bump 203 is formed onbond pad 104 at die 101. In some embodiments, first solder bump 203 isformed by a deposition process that is any of electroless plating,electrolytic plating (electroplating) or paste printing.

In the operation shown in FIG. 3C, second solder bump 204 is formed overfirst solder bump 203. In some embodiments, second solder bump 204 isformed by a deposition process that is any of electroless plating,electrolytic plating (e.g., electroplating) or paste printing. In someembodiments, second solder bump 204 has a relatively smaller volume thanfirst solder bump 203 to reduce the risk of solder bridge formationduring reflow, as described above. In some embodiments, the compositionof first solder bump 203 and second solder bump 204 are the same asdescribed above (e.g., FIG. 2D).

In the operation shown in FIG. 3D, bond pad 104 is juxtaposed with bondpad 105 to align second solder bump 204 with bond pad 105 on thesubstrate. In some embodiments, die 101 and substrate 102 are mounted onheated platens of a TCB tool head, where bond pads 104 and 105 face eachother, in preparation for a bonding operation such as flip-chip bonding(C4). Die 101 and substrate 102 are pressed together so that secondsolder bump 204 is pressed to bond pad 105 on the substrate. In someembodiments, the temperature of the TCB tool head is raised to T_(L2),the second liquidus temperature, liquefying and reflowing second solderbump 204. In some embodiments, solder from second solder bump 204 flowsover bond pad 105 and first solder bump 203, creating a partial solderjoint between first solder bump 203 and bond pad 105 on substrate 102.

As the partial solder joint is formed with first solder bump 203, thepartial solder joint may be relatively weak. However, the partial solderjoint is temporary and rigidly holds die 101 to substrate 102 duringsubsequent operations.

In the operation shown in FIG. 3E, CUF 206 is introduced. In someembodiments, CUF 206 is injected between die 101 and substrate 102. Insome embodiments, CUF 206 is introduced between die 101 and substrate102 by capillary action. Methods to introduce CUF 206 between die 101and substrate 102 are known in the industry, and may be employed tointroduce CUF 206.

In some embodiments, CUF 206 protects solder joints and contributes tostiffening the bond between die 101 and substrate 102, as describedabove. According to some embodiments, CUF 206 confines solder from firstsolder bump 203 from bridging over to neighboring solder bumps, asdescribed below.

In the operation shown in FIG. 3F, the temperature of the platens israised to the first liquidus temperature T_(L1) or above. First solderbump 203 liquefies and flows at or above T_(L1). Simultaneously, secondsolder bump 204 melts and reflows. In some embodiments, liquid solderfrom second solder bump 204 blends with liquid solder from first solderbump 203. In some embodiments, a compositional gradient forms duringreflow, where the elements in first solder bump 203 have a highestconcentration adjacent to bond pad 104 at die 101, with a lesseningconcentration toward bond pad 105 at substrate 102. Conversely, theelements of second solder bump 204 have a highest concentration adjacentto bond pad 105 at substrate 102, with a lessening concentration towardbond pad 104 at die 101. In some embodiments, the composition of thesolder homogenizes during reflow.

As the volume of first solder bump 203 is larger relative to the volumeof second solder bump 204, solder bridging would normally occur withoutthe presence of CUF 206. In some embodiments, CUF 206 confines liquidsolder from molten first solder bump 203 from flowing laterally. In someembodiments, solder bump 203 reflows and blends with solder bump 204, asdescribed above, forming permanent solder joint 207. In someembodiments, the platen temperature is ramped down to allow secondsolder bump to re-solidify.

FIG. 4 illustrates a cross-sectional view of a second embodiment ofpackage 400, having a dual solder joint embodiment between a die and asubstrate, without an underfill, according to some embodiments of thedisclosure.

In FIG. 4, package 400 comprises die 101, substrate 102. Die 101comprises bond pad 104, and substrate 102 comprises bond pad 105. Solderjoint 401 is bonded between bond pads 104 and 105. Solder joint 103 iscomposed of metallurgies that may comprise, but are not limited to,metals such as tin, silver, copper, bismuth, zinc, indium, gold,aluminum, and germanium. In some embodiments, solder joint 401 comprisesa compositional gradient of tin concentration between bond pad 104 andbond pad 105. In some embodiments, solder joint 401 comprises aconcentration of tin adjacent to bond pad 104 on die 101 that is higherthan the concentration of tin adjacent to bond pad 105 on substrate 102.

In some embodiments, an intermetallic compound (IMC) is formed at theinterface between bond pad 105 on substrate 102, and solder joint 401.In some embodiments, the IMC comprises copper and gold. In someembodiments, the IMC comprises copper and zinc. In some embodiments, theIMC comprises copper and silver. In some embodiments, the IMC comprisescopper and bismuth. In some embodiments, the IMC comprises copper andtin. In some embodiments, the IMC comprises copper and indium. In someembodiments, the IMC comprises copper and germanium. In someembodiments, the IMC has a melting temperature that is over 500° C.

FIGS. 5A-5D illustrate cross-sectional views, respectively, of a methodfor fabricating package 400, having a dual solder joint embodimentbetween a die and a substrate, without an underfill, according to someembodiments of the disclosure.

In the operation shown in FIG. 5A, substrate 102 is received havingfirst solder bump 203 deposited in an earlier operation over bond pad105. In some embodiments, first solder bump 203 is formed by adeposition process that is any of electroless plating, electrolyticplating (e.g., electroplating) or paste printing. In some embodiments,first solder bump 203 comprises a first solder metallurgy composition.In some embodiments, the first solder metallurgy composition comprisesmixtures comprising any of gold, aluminum, germanium, zinc, tin, bismuthand indium. An exemplary composition of first solder metallurgycomposition may comprise 80% gold and 20% tin. A second examplecomposition of first solder metallurgy may comprise 95% zinc and 5%aluminum. Here, the percentages are based on molar ratios. In someembodiments, first solder bump 203 has a first liquidus that ranges intemperature from 280° C. to 485° C. In some embodiments, the firstliquidus temperature (T_(L1)) of first solder bump 203 is dependent onthe composition of first solder bump 203.

In some embodiments, solder bump 203 is compressed to flatness(substantially flat profile) in a previous operation to reduce itsz-height to a predetermined value. In some embodiments, substrate 102 ismounted in a thermal compression bonding (TCB) tool and clamped betweenplatens. In some embodiments, first solder bump 203 is soft enough tocompress without application of heat. During compression, substrate 102is held flat, and first solder bump 203 is substantially planarized withother solder bumps on substrate 102. According to some embodiments, diebonding, such as flip-chip bonding, is facilitated as the probability ofcontact between individual solder bumps on substrate 102 and bond padsor bumps on a die is substantially increased during die (chip) bondingin a subsequent operation.

In the operation shown in FIG. 5B, intermetallic compound (IMC) 401 isformed by heating substrate 102 to temperatures below T_(L1), theliquidus temperature of first solder bump 203. An IMC is formed bythermally-driven inter-diffusion of atoms at an interface between twometals. In some embodiments, IMC 401 is formed from first solder bump203 by temperature cycling substrate 102 mounted in a TCB tool. In someembodiments, inter-diffusion of copper atoms from bond pad 105 intofirst solder bump 203 at the interface contributes to forming IMC 401.

In some embodiments, IMC 401 comprises copper and gold. In someembodiments, the IMC comprises copper and zinc. In some embodiments, IMC401 comprises copper and silver. In some embodiments, IMC 401 comprisescopper and bismuth. In some embodiments, the IMC comprises copper andtin. In some embodiments, IMC 401 comprises copper and indium. In someembodiments, IMC 401 has a melting temperature that is over 500° C.

In the operation shown in FIG. 5C, die 101 is received. In someembodiments, die 101 is bumped with second solder bump 204. In someembodiments, second solder bump 204 is formed by a deposition processthat is any of electroless plating, electrolytic plating (e.g.,electroplating) or paste printing. In some embodiments, second solderbump 204 comprises a second solder metallurgy composition. In someembodiments, the second solder metallurgy composition comprises metalssuch as, but not limited to, tin, silver, zinc, copper, bismuth andindium. An exemplary composition of second solder metallurgy compositionmay comprise 95.5% tin, 4% silver and 0.5% copper. A second examplecomposition of second solder metallurgy may comprise 89% tin, 8% zincand 3% bismuth. All percentages are based on molar ratios. In someembodiments, second solder bump 204 has a second liquidus (T_(L2)) thatranges in temperature from 138° C. to 227° C. In some embodiments, thesecond liquidus temperature is dependent on the composition of secondsolder bump 204.

In some embodiments, die 101 is aligned with substrate 102 and secondsolder bump 204 is juxtaposed with IMC 401. In some embodiments, die 101and substrate 102 are mounted in a heated TCB tool head. In someembodiments, second solder bump 204 is abutted against IMC 401 inpreparation for solder bonding.

In the operation shown in FIG. 5D, solder joint 402 is formed. In someembodiments, second solder bump 204 is reflowed by raising TCB headtemperature to temperatures at or above T_(L2), the liquidus temperatureof second solder bump 204. In some embodiments, solder joint 402 is apermanent solder joint, as IMC 401 has a melting point above 500° C.,and does not melt during reflow of second solder bump 204. In someembodiments, solder bump 204 has a volume small enough to form ameniscus over IMC 401 when liquefied, and does not flow laterally, andremains over IMC 401. In some embodiments, an underfill, such as CUF 206in FIGS. 3E and 3F, is not included, as the risk of solder bridgeformation is substantially reduced.

FIG. 6 illustrates a package having a dual solder joint embodimentbetween a die and a substrate, fabricated according to the disclosedmethod, as part of a system-on-chip (SoC) package in an implementationof computing device, according to some embodiments of the disclosure.

FIG. 6 illustrates a block diagram of an embodiment of a mobile devicein which flat surface interface connectors could be used. In someembodiments, computing device 600 represents a mobile computing device,such as a computing tablet, a mobile phone or smart-phone, awireless-enabled e-reader, or other wireless mobile device. It will beunderstood that certain components are shown generally, and not allcomponents of such a device are shown in computing device 600.

In some embodiments, computing device 600 includes a first processor610. The various embodiments of the present disclosure may also comprisea network interface within 670 such as a wireless interface so that asystem embodiment may be incorporated into a wireless device, forexample, cell phone or personal digital assistant.

In one embodiment, processor 610 can include one or more physicaldevices, such as microprocessors, application processors,microcontrollers, programmable logic devices, or other processing means.The processing operations performed by processor 610 include theexecution of an operating platform or operating system on whichapplications and/or device functions are executed. The processingoperations include operations related to I/O (input/output) with a humanuser or with other devices, operations related to power management,and/or operations related to connecting the computing device 600 toanother device. The processing operations may also include operationsrelated to audio I/O and/or display I/O.

In one embodiment, computing device 600 includes audio subsystem 620,which represents hardware (e.g., audio hardware and audio circuits) andsoftware (e.g., drivers, codecs) components associated with providingaudio functions to the computing device. Audio functions can includespeaker and/or headphone output, as well as microphone input. Devicesfor such functions can be integrated into computing device 600, orconnected to the computing device 600. In one embodiment, a userinteracts with the computing device 600 by providing audio commands thatare received and processed by processor 610.

Display subsystem 630 represents hardware (e.g., display devices) andsoftware (e.g., drivers) components that provide a visual and/or tactiledisplay for a user to interact with the computing device 600. Displaysubsystem 630 includes display interface 632 which includes theparticular screen or hardware device used to provide a display to auser. In one embodiment, display interface 632 includes logic separatefrom processor 610 to perform at least some processing related to thedisplay. In one embodiment, display subsystem 630 includes a touchscreen (or touch pad) device that provides both output and input to auser.

I/O controller 640 represents hardware devices and software componentsrelated to interaction with a user. I/O controller 640 is operable tomanage hardware that is part of audio subsystem 620 and/or displaysubsystem 630. Additionally, I/O controller 640 illustrates a connectionpoint for additional devices that connect to computing device 600through which a user might interact with the system. For example,devices that can be attached to the computing device 600 might includemicrophone devices, speaker or stereo systems, video systems or otherdisplay devices, keyboard or keypad devices, or other I/O devices foruse with specific applications such as card readers or other devices.

As mentioned above, I/O controller 640 can interact with audio subsystem620 and/or display subsystem 630. For example, input through amicrophone or other audio device can provide input or commands for oneor more applications or functions of the computing device 600.Additionally, audio output can be provided instead of, or in addition todisplay output. In another example, if display subsystem 630 includes atouch screen, the display device also acts as an input device, which canbe at least partially managed by I/O controller 640. There can also beadditional buttons or switches on the computing device 600 to provideI/O functions managed by I/O controller 640.

In one embodiment, I/O controller 640 manages devices such asaccelerometers, cameras, light sensors or other environmental sensors,or other hardware that can be included in the computing device 600. Theinput can be part of direct user interaction, as well as providingenvironmental input to the system to influence its operations (such asfiltering for noise, adjusting displays for brightness detection,applying a flash for a camera, or other features).

In one embodiment, computing device 600 includes power management 650that manages battery power usage, charging of the battery, and featuresrelated to power saving operation. Memory subsystem 660 includes memorydevices for storing information in computing device 600. Memory caninclude nonvolatile (state does not change if power to the memory deviceis interrupted) and/or volatile (state is indeterminate if power to thememory device is interrupted) memory devices. Memory subsystem 660 canstore application data, user data, music, photos, documents, or otherdata, as well as system data (whether long-term or temporary) related tothe execution of the applications and functions of the computing device600.

Elements of embodiments are also provided as a machine-readable medium(e.g., memory 660) for storing the computer-executable instructions. Themachine-readable medium (e.g., memory 660) may include, but is notlimited to, flash memory, optical disks, CD-ROMs, DVD ROMs, RAMs,EPROMs, EEPROMs, magnetic or optical cards, phase change memory (PCM),or other types of machine-readable media suitable for storing electronicor computer-executable instructions. For example, embodiments of thedisclosure may be downloaded as a computer program (e.g., BIOS) whichmay be transferred from a remote computer (e.g., a server) to arequesting computer (e.g., a client) by way of data signals via acommunication link (e.g., a modem or network connection).

Connectivity via network interface 670 includes hardware devices (e.g.,wireless and/or wired connectors and communication hardware) andsoftware components (e.g., drivers, protocol stacks) to enable thecomputing device 600 to communicate with external devices. The computingdevice 600 could be separate devices, such as other computing devices,wireless access points or base stations, as well as peripherals such asheadsets, printers, or other devices.

Network interface 670 can include multiple different types ofconnectivity. To generalize, the computing device 600 is illustratedwith cellular connectivity 672 and wireless connectivity 674. Cellularconnectivity 672 refers generally to cellular network connectivityprovided by wireless carriers, such as provided via GSM (global systemfor mobile communications) or variations or derivatives, CDMA (codedivision multiple access) or variations or derivatives, TDM (timedivision multiplexing) or variations or derivatives, or other cellularservice standards. Wireless connectivity (or wireless interface) 674refers to wireless connectivity that is not cellular, and can includepersonal area networks (such as Bluetooth, Near Field, etc.), local areanetworks (such as Wi-Fi), and/or wide area networks (such as WiMax), orother wireless communication.

Peripheral connections 680 include hardware interfaces and connectors,as well as software components (e.g., drivers, protocol stacks) to makeperipheral connections. It will be understood that the computing device600 could both be a peripheral device (“to” 682) to other computingdevices, as well as have peripheral devices (“from” 684) connected toit. The computing device 600 commonly has a “docking” connector toconnect to other computing devices for purposes such as managing (e.g.,downloading and/or uploading, changing, synchronizing) content oncomputing device 600. Additionally, a docking connector can allowcomputing device 600 to connect to certain peripherals that allow thecomputing device 600 to control content output, for example, toaudiovisual or other systems.

In addition to a proprietary docking connector or other proprietaryconnection hardware, the computing device 600 can make peripheralconnections 680 via common or standards-based connectors. Common typescan include a Universal Serial Bus (USB) connector (which can includeany of a number of different hardware interfaces), DisplayPort includingMiniDisplayPort (MDP), High Definition Multimedia Interface (HDMI),Firewire, or other types.

Reference in the specification to “an embodiment,” “one embodiment,”“some embodiments,” or “other embodiments” means that a particularfeature, structure, or characteristic described in connection with theembodiments is included in at least some embodiments, but notnecessarily all embodiments. The various appearances of “an embodiment,”“one embodiment,” or “some embodiments” are not necessarily allreferring to the same embodiments. If the specification states acomponent, feature, structure, or characteristic “may,” “might,” or“could” be included, that particular component, feature, structure, orcharacteristic is not required to be included. If the specification orclaim refers to “a” or “an” element, that does not mean there is onlyone of the elements. If the specification or claims refer to “anadditional” element, that does not preclude there being more than one ofthe additional element.

Furthermore, the particular features, structures, functions, orcharacteristics may be combined in any suitable manner in one or moreembodiments. For example, a first embodiment may be combined with asecond embodiment anywhere the particular features, structures,functions, or characteristics associated with the two embodiments arenot mutually exclusive.

While the disclosure has been described in conjunction with specificembodiments thereof, many alternatives, modifications and variations ofsuch embodiments will be apparent to those of ordinary skill in the artin light of the foregoing description. The embodiments of the disclosureare intended to embrace all such alternatives, modifications, andvariations as to fall within the broad scope of the appended claims.

In addition, well known power/ground connections to integrated circuit(IC) chips and other components may or may not be shown within thepresented figures, for simplicity of illustration and discussion, and soas not to obscure the disclosure. Further, arrangements may be shown inblock diagram form in order to avoid obscuring the disclosure, and alsoin view of the fact that specifics with respect to implementation ofsuch block diagram arrangements are highly dependent upon the platformwithin which the present disclosure is to be implemented (i.e., suchspecifics should be well within purview of one skilled in the art).Where specific details (e.g., circuits) are set forth in order todescribe example embodiments of the disclosure, it should be apparent toone skilled in the art that the disclosure can be practiced without, orwith variation of, these specific details. The description is thus to beregarded as illustrative instead of limiting.

The following examples pertain to further embodiments. Specifics in theexamples may be used anywhere in one or more embodiments. All optionalfeatures of the apparatus described herein may also be implemented withrespect to a method or process.

Example 1 is an apparatus comprising an integrated circuit (IC) packagehaving at least one solder bond pad, a die having at least one solderbond pad, wherein the die is bonded to the IC package by at least onesolder joint between the at least one bond pad of the die, and the atleast one bond pad of the IC package, and an underfill material betweenthe IC package and the die, wherein the at least one solder joint isembedded in the underfill material, and wherein the at least one solderjoint comprises a first metallurgy and a second metallurgy.

Example 2 includes all of the features of example 1, wherein the firstmetallurgy comprises one of: gold, aluminum, germanium, zinc, tin,bismuth or indium.

Example 3 includes all of the features of example 1, wherein the secondmetallurgy comprises any one of tin, silver, zinc, coper, bismuth orindium.

Example 4 includes all of the features of any one of examples 1 through3, wherein the at least one solder joint comprises a compositionalgradient, the compositional gradient comprising a higher concentrationof tin near the at least one bond pad of the die than near the at leastone bond pad of the IC package.

Example 5 includes all of the features of any one of examples 1 through3, wherein the at least one solder joint comprises a compositionalgradient, the compositional gradient comprising a higher concentrationof tin near the at least one substrate bond pad of the IC package thannear the at least one bond pad of the die.

Example 6 includes all of the features of any one of examples 1 through5, wherein a bump is over the at least one bond pad of the IC package,and wherein the top of the bump is substantially flat.

Example 7 includes all of the features of example 6, wherein the bumpcomprises an intermetallic compound comprising any one of gold, aluminumor germanium.

Example 8 is a system comprising a memory and a processor coupled to thememory, the processor comprising an integrated circuit (IC) packagehaving at least one solder bond pad; a die having at least one solderbond pad, wherein the die is bonded to the IC package by at least onesolder joint between the at least one bond pad of the die, and the atleast one bond pad of the IC package, and an underfill material betweenthe IC package and the die, wherein the at least one solder joint isembedded in the underfill material, and wherein the at least one solderjoint comprises a first metallurgy and a second metallurgy, wherein theprocessor is wirelessly coupled to an external device.

Example 9 includes all of the features of example 8, wherein the one ormore solder joints comprises an intermetallic compound over a IC packagesubstrate bond pad, the intermetallic compound comprising one of: copperand tin.

Example 10 includes all of the features of examples 8 or 9, wherein theat least one solder joint comprises a compositional gradient, thecompositional gradient comprising a higher concentration of tin near theat least one bond pad of the die than near the at least one bond pad ofthe IC package.

Example 11 includes all of the features of examples 8 or 9, wherein theat least one solder joint comprises a compositional gradient, thecompositional gradient comprising a higher concentration of tin near theat least one bond pad of the IC package than near the at least one bondpad of the die.

Example 12 includes all of the features of any one of examples 8 through11, wherein the first metallurgy comprises one of: gold, aluminum,germanium, zinc, tin, bismuth or indium.

Example 13 includes all of the features of any one of examples 8 through11, wherein the second metallurgy comprises any one of: tin, silver,zinc, copper, bismuth or indium.

Example 14 is an IC package, comprising at least one solder bond pad, adie having at least one solder bond pad, wherein the die is bonded tothe IC package by at least one solder joint between the solder bond padof the die and the solder bond pad of the IC package, wherein the atleast one solder joint comprises a first portion adjacent to a secondportion, wherein the first portion has a substantially flat profile, andwherein the first portion comprises a first metallurgy, and the secondportion comprises a second metallurgy, and an underfill material betweenthe IC package and the die, wherein the at least one solder joint isembedded in the underfill material, and wherein the at least one solderjoint comprises a first metallurgy and a second metallurgy.

Example 15 includes all of the features of example 14, wherein the firstportion of the solder joint has a substantially flat profile andcomprises an intermetallic compound, and wherein the intermetalliccompound comprises any one of gold, silver, copper, aluminum, zinc,bismuth, tin, indium, germanium.

Example 16 is a method comprising aligning a die to an IC package forbonding, wherein the die is pressed to the IC package, wherein a firstbond pad on the die is juxtaposed over a second bond pad on the ICpackage and an interface comprising a first layer having a first soldermetallurgy and a second layer having a second solder metallurgy isbetween a first bond pad on the die and a second bond pad on the ICpackage, and wherein the first layer is adjacent to the first bond padand the second layer is adjacent to the second bond pad, reflowing thefirst layer to form a partial solder joint between the first bond padand the second bond pad and reflowing the second layer to form acomplete solder joint between the first bond pad and the second bondpad, wherein the second reflow temperature is higher than the firstreflow temperature.

Example 17 includes all of the features of example 16, wherein theliquidus temperature of the first layer is lower than the liquidustemperature of the second layer.

Example 18 includes all of the features of examples 16 or 17, whereinaligning a die to an IC package substrate comprises depositing the firstlayer over the first bond pad, depositing the second layer over thesecond bond pad, flattening the second layer, juxtaposing the first bondpad over the second bond pad, and pressing the first bond pad to thesecond bond pad.

Example 19 includes all of the features of any one of examples 16through 18, wherein aligning a die to an IC package comprises depositingthe first layer over the first bond pad, depositing the second layerover the second bond pad, flattening the second layer, forming asaturated intermetallic compound between the second layer and the secondbond pad, juxtaposing the first bond pad over the second bond pad, andpressing the first bond pad to the second bond pad.

Example 20 includes all of the features of any one of examples 16through 19, wherein aligning a die to an IC package substrate comprisesdepositing the first layer over the first bond pad, depositing thesecond layer over the second bond pad, flattening the second layer,juxtaposing the first bond pad over the second bond pad, and pressingthe first bond pad to the second bond pad.

Example 21 includes all of the features of any one of examples 16through 20, wherein reflowing the first layer to form a partial solderjoint between the first bond pad and the second bond pad comprisesreflowing the first layer at a first reflow temperature.

Example 22 includes all of the features of any one of examples 16through 21, wherein reflowing the second layer to form a complete solderjoint between the first bond pad and the second bond pad comprisesreflowing the second layer at a second reflow temperature, wherein thesecond reflow temperature is higher than the first reflow temperature.

Example 23 includes all of the features of any one of examples 16through 22, further comprising injecting a capillary underfill materialbetween the die and the IC package substrate to embed the partial solderjoint, and curing the capillary underfill material.

Example 24 includes all of the features of any one of examples 20through 23, wherein depositing the second layer over the second bond padcomprises one of electroless plating, electrolytic plating or pasteprinting.

Example 25 includes all of the features of any one of examples 16through 24, wherein pressing the first bond pad to the second bond padcomprises pressing the die to the IC package substrate in athermocompression bonding tool.

An abstract is provided that will allow the reader to ascertain thenature and gist of the technical disclosure. The abstract is submittedwith the understanding that it will not be used to limit the scope ormeaning of the claims. The following claims are hereby incorporated intothe detailed description, with each claim standing on its own as aseparate embodiment.

What is claimed is:
 1. An apparatus, comprising: an integrated circuit(IC) package substrate comprising at least one first bond pad; a diecomprising at least one second bond pad, wherein the die is bonded tothe IC package substrate by at least one solder joint between the firstand second bond pads; and an underfill material between the IC packagesubstrate and the die, wherein the solder joint is embedded in theunderfill material, and wherein the solder joint comprises first andsecond compositional gradients across a thickness of the solder joint,the first compositional gradient comprising a higher concentration oftin adjacent the first bond pad and lessening to a lower concentrationadjacent the second bond pad and the second compositional gradientcomprising a higher concentration of one of gold or zinc adjacent thesecond bond pad and lessening to a lower concentration adjacent thefirst bond pad.
 2. The apparatus of claim 1, wherein the secondcompositional gradient comprises a gradient of gold and the solder jointfurther comprises silver and copper.
 3. The apparatus of claim 1,wherein the second compositional gradient comprises a gradient of goldand the solder joint further comprises zinc and bismuth.
 4. Theapparatus of claim 1, wherein the second compositional gradientcomprises a gradient of zinc and the solder joint further comprisesaluminum.
 5. The apparatus of claim 1, wherein the second compositionalgradient comprises a gradient of zinc and the solder joint furthercomprises bismuth.
 6. The apparatus of claim 1, wherein the solder jointcomprises an intermetallic compound comprising any one of gold, silver,copper, aluminum, zinc, bismuth, tin, indium, or germanium.
 7. A system,comprising: a memory; and a processor coupled to the memory, theprocessor comprising: an integrated circuit (IC) package substratecomprising at least one first bond pad; a die comprising at least onesecond bond pad, wherein the die is bonded to the IC package substrateby at least one solder joint between the first and second bond pads; andan underfill material between the IC package substrate and the die,wherein the solder joint is embedded in the underfill material, andwherein the solder joint comprises first and second compositionalgradients across a thickness of the solder joint, the firstcompositional gradient comprising a higher concentration of tin adjacentthe first bond pad and lessening to a lower concentration adjacent thesecond bond pad and the second compositional gradient comprising ahigher concentration of one of gold or zinc adjacent the second bond padand lessening to a lower concentration adjacent the first bond pad. 8.The system of claim 7, wherein the second compositional gradientcomprises a gradient of gold and the solder joint further comprisessilver and copper.
 9. The system of claim 7, wherein the secondcompositional gradient comprises a gradient of gold and the solder jointfurther comprises zinc and bismuth.
 10. The system of claim 7, whereinthe second compositional gradient comprises a gradient of zinc and thesolder joint further comprises aluminum.
 11. The system of claim 7,wherein the second compositional gradient comprises a gradient of zincand the solder joint further comprises bismuth.
 12. The system of claim7, wherein the solder joint comprises an intermetallic compoundcomprising any one of gold, silver, copper, aluminum, zinc, bismuth,tin, indium, or germanium.
 13. An apparatus, comprising: an integratedcircuit (IC) package substrate comprising at least one first bond pad; adie comprising at least one second bond pad, wherein the die is bondedto the IC package substrate by at least one solder joint between thefirst and second bond pads of the IC package, wherein solder jointcomprises first and second compositional gradients across a thickness ofthe solder joint, the first compositional gradient comprising a higherconcentration of one of gold or zinc adjacent the first bond pad andlessening to a lower concentration adjacent the second bond pad and thesecond compositional gradient comprising a higher concentration of tinadjacent the second bond pad and lessening to a lower concentrationadjacent the first bond pad; and an underfill material between the ICpackage substrate and the die, wherein the solder joint is embedded inthe underfill material.
 14. The apparatus of claim 13, wherein thesecond compositional gradient comprises a gradient of gold and thesolder joint further comprises silver and copper.
 15. The apparatus ofclaim 13, wherein the second compositional gradient comprises a gradientof gold and the solder joint further comprises zinc and bismuth.
 16. Theapparatus of claim 13, wherein the second compositional gradientcomprises a gradient of zinc and the solder joint further comprisesaluminum.
 17. The apparatus of claim 13, wherein the secondcompositional gradient comprises a gradient of zinc and the solder jointfurther comprises bismuth.
 18. The apparatus of claim 13, wherein thesolder joint comprises an intermetallic compound comprising any one ofgold, silver, copper, aluminum, zinc, bismuth, tin, indium, orgermanium.